Marine Chemistry最新文献

{"title":"Samarium (Sm3+) and copper (Cu2+) complexation property with dissolved organic matter","authors":"Nabila Abbad ,&nbsp;Roland Redon ,&nbsp;Benjamin Oursel ,&nbsp;Christophe Lepoupon ,&nbsp;Gaël Durrieu ,&nbsp;Houssam Hajjoul ,&nbsp;Stéphane Mounier","doi":"10.1016/j.marchem.2025.104514","DOIUrl":"10.1016/j.marchem.2025.104514","url":null,"abstract":"<div><div>This study investigates the speciation of Samarium (III) in the presence of natural organic matter, standard humic and fulvic acids from the Suwannee River. Fluorescence quenching and Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) were employed to analyze various samples, using logarithmic additions of Sm³⁺ and Cu²⁺. The 1 L:1 M and 1 L:1 M:H models were applied to account for pH effects, yielding pH-independent complexant parameters K_Sm and K_Cu as well as <span><math><msub><mi>C</mi><msub><mi>L</mi><mi>Sm</mi></msub></msub><mspace></mspace><mi>and</mi><mspace></mspace><msub><mi>C</mi><msub><mi>L</mi><mi>Cu</mi></msub></msub></math></span>that revealed specific binding sites. A notably higher affinity was observed for humic acids with Sm³⁺ compared to Cu²⁺. The logarithms of the complexation constant for the Sm³⁺ were 5.4, 5.2 and 4.7 for SRNOM, SRHA and SRFA, respectively. Fluorescence quenching analyses identified two distinct fluorescent components related to dissolved organic matter, showing different affinities for Sm³⁺ and Cu²⁺ that varied with pH. Humic acids exhibited the highest complexation capacity for Sm³⁺, attributed to their structural properties, with complexation capacities of 4.77 10⁻⁴, 0.82 and 4.46 10⁻³ mol of Sm per g of SRNOM, SRHA and SRFA, respectively. Temporal deconvolution of fluorescence responses revealed a tri-exponential decay with three lifetimes (τ₁, τ₂ and τ₃) remaining relatively constant during Sm³⁺ or Cu²⁺ titrations, confirming that the fluorescence quenching is primarily a static mechanism. Speciation modeling demonstrated a shift from humic-associated complexes in freshwater to carbonate complexes in seawater as salinity increases. These findings highlight the importance of accurately characterizing DOM complexation properties to understand the environmental behavior of trace metals, particularly in response to salinity and carbon concentration gradients in estuarine systems.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104514"},"PeriodicalIF":3.0,"publicationDate":"2025-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143738842","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Influence of seasonal changes in organic matter pool on copper bioavailability in a stratified estuary","authors":"Saša Marcinek,&nbsp;Ana-Marija Cindrić,&nbsp;Dario Omanović","doi":"10.1016/j.marchem.2025.104513","DOIUrl":"10.1016/j.marchem.2025.104513","url":null,"abstract":"<div><div>This work presents a detailed analysis of seasonal changes in copper (Cu) organic speciation and its bioavailability in the Krka River estuary, a highly stratified microtidal system characterized by low riverine input of dissolved organic matter (DOM) and trace metals but experiencing heightened anthropogenic Cu pressures during summer as a result of increased touristic activities. Total dissolved Cu concentrations ranged from 3.4 nmol L⁻¹ in winter up to 25.8 nmol L⁻¹ in summer, with substantial summer increase limited to water layer above the halocline. Two distinct ligand classes were identified in all samples, with conditional stability constants of log<em>K</em>’₁ = 13.2 ± 0.5 and log<em>K</em>’₂ = 11.2 ± 0.4. Dissolved organic carbon (DOC) and concentrations of both ligand classes were higher in summer than in winter, with strong indications of their in situ production driven by enhanced primary production and/or intensified microbial activity. In winter, despite the low DOC levels (avg 63.3 μmol L⁻¹), DOM above the halocline showed pronounced terrestrial signature with higher density of Cu-binding sites compared to DOM in summer with nearly twice as high DOC levels (avg 113.5 μmol L⁻¹). The results suggest that terrestrial humic substances (HS) dominated the ligand pool in these waters during winter (estimated 80 % of total ligand pool), possibly contributing to both ligand classes. While HS remained an important fraction of the ligand pool in the summer (estimated 30 % of total ligand pool), the terrestrial signature of DOM in this season was minimal, pointing to their production within the estuary. The summer increase in ligand concentrations above the halocline was accompanied by a reduction in their binding strengths (by approximately 0.5 log units) compared to winter, along with a decrease in DOM molecular weight, possibly influenced by solar irradiation. Seasonal anthropogenic Cu input was successfully buffered by the ambient ligand pool, keeping the concentration of free Cu-ions, its most bioavailable specie, well below documented toxicity levels for Cu (maximum of 2.54 pmol L⁻¹). The seasonal DOM variations resulted in a ∼ two-fold increase in the Cu-binding capacity in summer (33 nmol L⁻¹) compared to winter (17 nmol L⁻¹). Despite the increased buffering capacity in summer, Cu levels are approaching this safety limit, which may increase its bioavailability to a concerning level, a risk much lower in winter when Cu inputs are minimal. These results underscore the critical role of DOM in mitigating seasonal anthropogenic Cu inputs, while also highlighting the need for further investigation into the long-term resilience of estuarine systems under shifting environmental and anthropogenic pressures.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104513"},"PeriodicalIF":3.0,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143682117","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Diatom-driven processes lead to the assimilation of elements from silicate minerals into their frustules","authors":"Tasuku Akagi,&nbsp;Sophia Welti,&nbsp;Rei Tajiri,&nbsp;Kazuhiko Shimada","doi":"10.1016/j.marchem.2025.104512","DOIUrl":"10.1016/j.marchem.2025.104512","url":null,"abstract":"<div><div>To examine whether diatoms dissolve silicate minerals and incorporate foreign metals into their frustules, culture experiments were performed using <em>Achnanthes kuwaitensis</em> Hendey, <em>Eucampia</em> sp. and <em>Coscinodiscus wailesii</em>. These comprised two comparative experiments: (i) an analysis of diatom activities (population, transparent exopolymer particles (TEP) secretion and the Al/Si of frustules) in the presence/absence of feldspar particles, and (ii) an examination of mineral surfaces in the presence/absence of diatoms. Although the presence/absence of silicate minerals did not incur marked differences in diatom population, TEP secretion increased in the presence of silicate particles. Further, it was observed that the girdles of <em>Coscinodiscus</em> frustules showed double Si peaks and the outer layers of the girdles had significantly higher Al/Si ratios than the inner layers when feldspar particles were present. In the diatom cultures, feldspar particles largely disappeared in extended cultivation, and those still present showed rounded or fractured edges, features that were not seen in the absence of diatoms. The presence of diatoms appeared to have more influence on silicate minerals than the presence of silicate minerals on diatom activities. The C/Si ratios of the rounded feldspar grain edges in the <em>Coscinodiscus</em> cultures were significantly higher than those of stepwise edges, that we interpret to indicate that diatoms secrete TEP to dissolve silicate minerals. Two observations substantiated this hypothesis: pH decreases around diatoms, and incorporation of the mineral particles in TEP coatings.</div><div>Nevertheless, the physiological advantage for diatoms to dissolve silicate minerals remains unclear. Given the difference in TEP secretion between two different feldspar minerals, we believe that diatoms actively dissolve silicates in order to incorporate silica. We thus propose a mechanism by which diatoms dissolve silicate minerals. This may explain the inclusion of foreign elements at levels, whose relative concentrations are similar to those in terrigenous matter, in diatom frustules.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104512"},"PeriodicalIF":3.0,"publicationDate":"2025-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143760083","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Regression-based characterization of the marine carbonate system across shelf and nearshore waters of Queen Charlotte Sound","authors":"A.A. Hare ,&nbsp;W. Evans ,&nbsp;H.V. Dosser ,&nbsp;J.M. Jackson ,&nbsp;S.R. Alin ,&nbsp;C. Hannah ,&nbsp;T. Ross ,&nbsp;J.M. Klymak","doi":"10.1016/j.marchem.2025.104511","DOIUrl":"10.1016/j.marchem.2025.104511","url":null,"abstract":"<div><div>Marine carbonate system measurements are essential for understanding ocean acidification and CaCO₃ saturation states, and their response to oceanographic and anthropogenic processes. Acquiring such measurements in remote coastal areas is limited by challenges in the development and deployment of autonomous sensors for these parameters, and by the complexity and costs of directly measuring them. We address this challenge by extending an established method of estimating carbonate system parameters through proxy variables to the remote waters of Queen Charlotte Sound, British Columbia. Paired regressions are developed from bottle samples and common hydrographic measurements for both offshore and coastal waters that intersect in this region but retain distinct relationships between total alkalinity and salinity. Application of these regression models to regional autonomous glider data demonstrates that established features of this shelf system can be characterized from a carbonate system perspective along a contiguous transect from land to the shelf break, despite greater regression uncertainties in coastal water. These results also provide new insight into the dynamics of aragonite saturation on the shelf in relation to regional winds. This approach extends a tool to gain knowledge of the marine carbonate system to a coastal region of the northeast Pacific Ocean where hydrographic data used as proxies are more commonly available.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104511"},"PeriodicalIF":3.0,"publicationDate":"2025-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143682113","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Copper speciation in a tropical mangrove forest of Southeast Asia","authors":"Ying Ping Lee ,&nbsp;Kuo Hong Wong ,&nbsp;Hajime Obata ,&nbsp;Mohd Zaki Kamsah ,&nbsp;Mohd Hisyam Rasidi","doi":"10.1016/j.marchem.2025.104510","DOIUrl":"10.1016/j.marchem.2025.104510","url":null,"abstract":"<div><div>Mangrove forests are vital ecosystems that protect coastlines, sequester carbon, and support diverse food webs. Elucidation of the behaviors of nutrients, trace elements, and organic matters in these regions is crucial to understand the impact of human activities and the potential effects of climate change. In this study, we revealed the distributions and bioavailability of a trace metal, copper (Cu), and conducted the first study of Cu speciation in a mangrove region in Southeast Asia. Dissolved Cu (dCu) concentrations ranged from 0.3 to 2.3 nmol L⁻¹ in the study region, which are relatively low compared to most other coastal regions globally. Two classes of Cu-binding organic ligands with average conditional stability constants, log K, of 15.5 and 13.2, respectively, were detected in mangrove waters. Complexing capacities of the ligands generally decrease in low salinity waters with low dCu concentrations. Concentrations of the stronger-binding class of organic ligand (L₁) were higher than those of dCu, reducing the bioavailable Cu²⁺ concentration to less than femtomolar levels, potentially inducing Cu-limitation to microorganism growth. To further understand the biogeochemical processes of trace metals in mangrove regions, future studies should prioritize obtaining baseline data using standardized sampling and analytical techniques to ensure consistent and reliable results.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104510"},"PeriodicalIF":3.0,"publicationDate":"2025-03-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143628133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Surface macro- and micro-nutrients within the Copper River plume region respond to along-shore winds","authors":"E.L.S. Ortega,&nbsp;I. Reister,&nbsp;S.L. Danielson,&nbsp;A.M. Aguilar-Islas","doi":"10.1016/j.marchem.2025.104508","DOIUrl":"10.1016/j.marchem.2025.104508","url":null,"abstract":"<div><div>The Copper River is a major source of freshwater to the Northern Gulf of Alaska (NGA) shelf with a seasonal cycle that reaches peak discharge in summer. This glacially-fed river also provides a large input of dissolved chemicals to the NGA, and because of its large particle load, it impacts the distribution of particle-reactive elements. Summertime sampling of shelf water properties was carried out within the Copper River plume region during two years: first during a period of upwelling-favorable winds and higher river discharge (4–7 July 2019) and later during lower river discharge and more typical downwelling conditions (11–13 July 2020). Although these wind conditions were observed in separate years, both can occur over the course of a single summer. We found that the export of most nutrients to surface shelf waters was enhanced under upwelling-favorable winds accompanied by higher river discharge compared to downwelling conditions and lower discharge. For example, greater cross-shelf plume transport in 2019 resulted in higher mid-shelf surface inventories for nitrate + nitrite (N + N), silicic acid (H₄SiO₄), phosphate (PO₄³⁻), dissolved Fe (dFe), and dissolved Cu (dCu) compared to 2020. Entrainment of relatively macronutrient-rich subsurface waters under upwelling conditions may also have contributed to the enhancement of these mid-shelf nutrient inventories. The observed high N:P ratios in plume waters were likely driven by the scavenging of P within particle-laden plume waters. Similarly, we observed lower than expected [dFe] (1.58 to 6.12 nM) in particle-laden plume waters, likely a result of enhanced scavenging combined with low concentrations of dissolved Fe-binding ligands. Although dNi and dZn have a river source, we observed lower concentrations in surface shelf waters under upwelling conditions, suggesting enhanced dilution by relatively micronutrient-poor subsurface waters. Results highlight the influence of sub-seasonal variations in atmospheric forcing on nutrient distributions and suggest that this forcing also impacts the location and timing of primary production hotspots during summer, adding to the ecological mosaic of the NGA across a range of temporal and spatial scales.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104508"},"PeriodicalIF":3.0,"publicationDate":"2025-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143510835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Comparative study of dissolved copper speciation using DGT and CLE-AdSV in a contaminated urban river estuary and marina","authors":"Billie G.B. Benedict ,&nbsp;Rebecca Zitoun ,&nbsp;Keith A. Hunter ,&nbsp;Sylvia G. Sander","doi":"10.1016/j.marchem.2025.104500","DOIUrl":"10.1016/j.marchem.2025.104500","url":null,"abstract":"<div><div>A comprehensive study was conducted in a river estuary and marina in Auckland, New Zealand, to examine the <em>in-situ</em> speciation of copper (Cu) complexes across freshwater, estuarine, and marine environments using the diffusive gradient in thin films (DGT) technique. The study employed both open-pore (OP) and restrictive-pore (RP) diffusive gels of varying thicknesses to assess the effectiveness of DGT hydrogels and the role of the apparent diffusive boundary layer (ADBL) in determining the lability of Cu complexes in natural waters. The DGT findings were compared with results from competing ligand exchange–adsorptive stripping voltammetry (CLE-AdSV) and a speciation prediction model (WHAM/Model-VII). The study highlighted the critical importance of accounting for the ADBL, as its exclusion led to an average underestimation of Cu-complex lability by approximately 50 %. Given the minimal difference in outcomes between DGT-OP and DGT-RP, the use of standard DGT-OP is recommended. Further analysis revealed a strong correlation between DGT-labile Cu (CuDGT-lab), the weaker Cu-L₂ complexes detected by CLE-AdSV, and the inorganic Cu species predicted by WHAM/Model-VII, the latter two based on discrete samples. A strong relationship was also noted between Cu_DGT-lab and the inorganic Cu measured by CLE-AdSV. The study provided compelling evidence that the <em>in-situ</em> ligand pool consists of a mixture of terrestrial humic substances and marine-derived organic ligands. These marine ligands form highly stable Cu-L₁ complexes along the salinity gradient, which were mostly DGT-inert. The DGT results indicated that the lability of <em>in-situ</em> Cu complexes decreased with increasing salinity, with over 60 % of Cu in freshwater being DGT-labile. Overall, the study demonstrates that the DGT technique is a robust and straightforward method for environmental monitoring and risk assessment across diverse physico-chemical water conditions.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"270 ","pages":"Article 104500"},"PeriodicalIF":3.0,"publicationDate":"2025-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143508084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Excess alkalinity and its impacts on pCO2 estimation in coastal and estuarine waters of the Yellow Sea","authors":"Young Ho Ko ,&nbsp;Seung-Hee Shin ,&nbsp;Seong-Gil Kim ,&nbsp;Mi-Ok Park ,&nbsp;Min-Woo Seok ,&nbsp;Min-Soo Kim ,&nbsp;Kitack Lee ,&nbsp;Tae-Wook Kim","doi":"10.1016/j.marchem.2025.104499","DOIUrl":"10.1016/j.marchem.2025.104499","url":null,"abstract":"<div><div>Excess alkalinity (TA_EX) represents an uncharacterized component of total alkalinity (TA), which can introduce significant uncertainty in the estimation of other carbonate parameters. This effect is particularly pronounced in productive coastal regions, where the use of measured TA as an input parameter may lead to inaccurate assessment. In this study, we evaluated the seasonal variability of TA_EX along the western coast of South Korea by applying an overdetermination method, which allows for the quantification of discrepancies (i.e., TA_EX) between measured TA and values calculated from pH and dissolved inorganic carbon (DIC). Samples with salinity below 20 were excluded due to difficulties in accurately quantifying uncertainties in TA_EX calculations, which increase significantly below this threshold. Elevated TA_EX concentrations were found in waters with salinity below 25, with some instances exhibiting TA_EX values reaching up to 50 μmol kg⁻¹, suggesting riverine influence. Additionally, elevated TA_EX values (&gt; 20 μmol kg⁻¹) were also observed in locations markedly undersaturated with respect to atmospheric CO₂, indicating contributions from in-situ biological production. The high TA_EX values associated with increased water transparency during autumn and winter months suggested that light penetration may significantly enhance biological activity, subsequently increasing TA_EX levels. These findings highlight the importance of riverine inputs and biological processes in shaping the spatial and temporal distribution of TA_EX. In the study area, TA_EX should be accounted for in seawater partial pressure of CO₂ (<em>p</em>CO₂) calculations using the DIC–TA pair, as TA_EX significantly influences these calculations compared to the pH–TA and pH–DIC pair.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"269 ","pages":"Article 104499"},"PeriodicalIF":3.0,"publicationDate":"2025-02-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143427906","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Achieving measurement comparability in mercury speciation analysis in seawater: Key requirements and best practices","authors":"Igor Živković ,&nbsp;Lars-Eric Heimbürger-Boavida ,&nbsp;Mariia V. Petrova ,&nbsp;Aurélie Dufour ,&nbsp;Ermira Begu ,&nbsp;Milena Horvat","doi":"10.1016/j.marchem.2025.104498","DOIUrl":"10.1016/j.marchem.2025.104498","url":null,"abstract":"<div><div>The comparability of measurement results is an important issue in contemporary mercury (Hg) speciation in seawater. Sampling campaigns must be properly designed to determine significant differences on spatial and temporal scales, considering two major parameters: the variability of expected data at a given sampling point/transect and variability in the results due to the intrinsic properties of specific analytical methods, particularly the measurement uncertainty. This study assessed the required sample size, considering several aspects of data variability when determining total Hg, dissolved gaseous Hg, and methylated Hg species in seawater. The required sample sizes were calculated using (1) the measurement uncertainty of a single-laboratory measurement of analytical methods used; (2) performance of the laboratories in interlaboratory comparison exercises; and (3) natural variability in Hg species/fractions in a selected case study in the Central Adriatic Sea. It was shown that the measurement uncertainty of a particular method and interlaboratory variability among laboratories have significant influence on data interpretation in case natural variability of Hg fractions is relatively small, such as for example the open seawater depth profiles. In contrary, in areas with large natural variability of Hg contractions, such as coastal and contaminated sites, their influence on data interpretation is negligible. The present paper introduces the importance of proper estimation of measurement uncertainty in international programs, such as GEOTRACES, where data comparability is of fundamental importance to assess temporal and spatial trends of Hg measurements in the marine environment.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"269 ","pages":"Article 104498"},"PeriodicalIF":3.0,"publicationDate":"2025-02-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143350669","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Vertical biochemical composition of particulate organic matter in the Seychelles-Chagos Thermocline Ridge (SCTR), southwestern Indian Ocean","authors":"Sanghoon Park ,&nbsp;Yejin Kim ,&nbsp;Jaesoon Kim ,&nbsp;Jae Ha Jeon ,&nbsp;Inhee Lee ,&nbsp;Doshik Hahm ,&nbsp;Dong-Jin Kang ,&nbsp;Sang Heon Lee","doi":"10.1016/j.marchem.2025.104496","DOIUrl":"10.1016/j.marchem.2025.104496","url":null,"abstract":"<div><div>The Seychelles-Chagos Thermocline Ridge (SCTR) in the southwestern Indian Ocean is characterized by upwelling-driven nutrient enrichment and enhanced biological activity compared to adjacent non-SCTR regions. This study investigated the vertical distribution and biochemical composition of particulate organic matter (POM) within these contrasting environments. The SCTR featured a shallower thermocline and cooler sea surface temperatures, indicative of upwelling, which correlated with significantly higher chlorophyll-<em>a</em> concentrations (<em>t</em>-test, <em>p</em> &lt; 0.05). A notable dominance of micro-sized phytoplankton was observed in the SCTR, contributing 13.6 ± 3.0 % of the total phytoplankton biomass, compared to 5.6 ± 1.6 % in the non-SCTR. CHEMTAX analysis revealed distinct phytoplankton communities, with diatoms being approximately four times more abundant in the SCTR (16.5 ± 4.5 %) than in the non-SCTR (4.2 ± 1.2 %). Meanwhile, <em>Prochlorococcus</em> dominated both regions but contributed less in the SCTR (25.2 ± 3.9 %) than non-SCTR (46.8 ± 7.1 %). The biological macromolecular composition of POM showed clear regional differences, with lipid concentrations in the SCTR's photic layer significantly higher (61.3 μg L⁻¹) than in the non-SCTR (23.4 μg L⁻¹). Total biological macromolecule concentrations in the SCTR's photic zone was more than double that of the non-SCTR (96.3 μg L⁻¹ vs. 40.9 μg L⁻¹), reflecting enhanced biological productivity. Elevated macromolecule concentrations were also detected in the aphotic layer of the SCTR. Notably, the less pronounced decline in the protein-to-carbohydrate ratio from photic to aphotic layers in the SCTR suggests that POM sinking to the deep ocean in this region is relatively fresher and less degraded, indicating a more efficient biological carbon pump and enhanced potential for carbon sequestration. These findings highlight the SCTR as a key region of elevated biological productivity and distinct environmental mechanisms driving biogeochemical cycling, providing critical insights into organic matter preservation and carbon export processes in tropical upwelling systems and their role in global marine ecosystems.</div></div>","PeriodicalId":18219,"journal":{"name":"Marine Chemistry","volume":"269 ","pages":"Article 104496"},"PeriodicalIF":3.0,"publicationDate":"2025-01-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143092363","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}